Cable pulling is a commonly used technique whereby a pulling rope is attached to a cable or wire that is to be pulled through conduit by a cable puller. The pulling rope is wound by a user around a capstan and tails off the capstan. The capstan is powered by a motor and acts as a frictional force multiplier. The motor and capstan are usually referred to as being part of the puller head of the cable puller. Use of the cable puller to pull the cable through the conduit allows the user to exert only a small force on the rope that tails off of the capstan. This relatively small force is translated into a large force of several thousand pounds which is exerted on the incoming pulling rope and which provides enough force on the pulling rope and the cable to pull them through the conduit. Typically, cable pullers have a conduit attachment device that extends from a boom which is attached to the puller head. The conduit attachment device allows the cable puller to be rigidly secured to the conduit from which the pulling rope and/or cable are to be pulled. The most frequent orientation encountered in cable pulling is the situation where the rope or cable is pulled upward out of the conduit, however, sometimes the opening of the conduit faces downward. In this situation, the cable must be pulled downward out of the conduit. Consequently, there has been a need for cable pullers to be able to pull in either of two modes of operation, an upward pulling mode of operation or a downward pulling mode of operation.
One technique to effectuate the conversion from upward to downward pulling is to flip the entire cable pulling assembly upside down so that the puller head, boom, and conduit attachment device are reversed in spatial orientation to the user and the environment. Once the cable puller has been attached to the conduit, a downward cable pull is possible because the orientation of the capstan to the conduit attachment system and any pulleys or sheaves in between them is the same as when an upward cable pull is being performed. Although this technique works, it has the considerable drawback that the user has to move heavy components until they are upside down. This technique can be extremely time consuming and burdensome. It is particularly difficult to invert large cable pullers which are used to exert forces in the range of thousands of pounds.
Another technique to change the direction of pulling cable has been to provide an additional pulley or sheave located somewhere along the length of the boom between the conduit attachment system and the puller head. This technique provides several disadvantages. To begin, it requires the addition of an extra part thereby increasing the cost of the cable puller. In addition, the interaction between the rope or cable and the additional pulley or sheave creates extra drag and friction which makes pulling the cable more difficult. Another disadvantage provided by the addition of another pulley or sheave is that extra time is needed to feed the pulling rope around the additional pulley or sheave. Finally, use of an extra pulley or sheave introduces an extra step to the cable puller, complicating use of the device and providing another opportunity for user error.
Still another technique used to convert a cable puller from an upward pulling position to a downward pulling position is to provide an idler wheel in front of the cable puller's capstan to interchange the side of the boom on which the rope or cable is positioned. For example, to perform an upward pull, typically the rope is positioned on the top side of the boom but if a downward pull is to be performed, the user typically routes the rope about the idler wheel so that the rope is positioned on the lower side of the boom. This technique, however, also suffers from the cost and time consumption disadvantages discussed for the previous techniques.
Therefore, a need for a method for switching between upward and downward cable pulling that is less time consuming, more cost effective, and more efficient than has been previously devised still exists.
The present invention provides a cable puller which overcomes the problems presented in the prior art and which provides additional advantages over the prior art. Such advantages will become clear upon a reading of the attached specification in combination with a study of the drawings.